During the Investigation of a New Type of Optical Fiber $n = 1.21 )$

Multiple Choice

During the investigation of a new type of optical fiber having an index of refraction $n = 1.21 )$ a laser beam is aimed at the flat end of a straight fiber,as shown in the figure.What is the maximum angle of incidence θ₁ if the beam is not to escape from the sides of the fiber if it is surrounded by air?

A) 42.9°
B) 39.8°
C) 36.7°
D) 33.6°
E) 30.5°